喷雾机喷杆压力损失及对喷雾质量的影响

运用流体力学理论,对喷雾机喷杆压力损失进行了分析。在对喷杆中液体的流动模型作出假设的基础上,结合具体参数分析了喷杆中的液流状态,确定了喷杆压力损失的范围。确定了ALLMAN200型喷杆式喷雾机单个喷杆上压力损失的范围,用实验对计算结果进行了验证。利用激光粒度仪研究了压力损失对XR系列喷头雾滴径谱分布的影响,指出压力损失对喷雾质量的影响程度应根据具体条件确定,不能一概忽略不计。     

宁夏中部干旱带压砂地西甜瓜种植业发展的支撑保障体系研究

在阐述压砂西甜瓜产业发展特点、深入分析产业发展中存在问题的基础上,构建了西甜瓜产业发展的政策保障体系、技术保障体系、资金保障体系、社会化服务体系、质量安全保障体系,并提出了相应的建议,以期推动该产业的可持续发展。     

Aerodynamic analysis and CFD simulation of several cellulose evaporative cooling pads used in Mediterranean greenhouses

The present work makes an aerodynamic analysis and computational fluid dynamics (CFD) simulation of the four commercial models of corrugated cellulose evaporative cooling pads that are most widely used in Mediterranean greenhouses. The geometric characteristics of the pads have been determined as well as the volume of water they retain at different flows of water, thus obtaining the mean thickness of the sheet of water which runs down them and their porosity. By means of low velocity wind tunnel experiments, the pressure drop produced by the pads has been recorded at different wind speeds and water flows. In this way it has been possible to obtain the relationship of the permeability and the inertial factor with pad porosity using a cubic type equation. Finally, a CFD simulation with a 3D model has been carried out for both dry pads (Q_w = 0 l s⁻¹ m⁻²) and wet ones (Q_w = 0.256 l s⁻¹ m⁻²), finding good correlation between the simulated and experimental pressure drop, with maximum differences of 9.08% for dry pads and 15.53% for wet ones at an airspeed of 3 m s⁻¹.     

甘肃省不同生态区耕地压力差异研究

从甘肃省不同生态区入手,采用耕地压力指数模型,对全省耕地压力进行测算,并建立全省耕地压力指数与人均GDP及产业结构的回归模型,比较了各生态区耕地压力的差距。结果表明,甘肃省1978~2006年耕地压力呈先递减后增长的变化趋势,人均GDP呈快速增长的趋势;各生态区除河西区外,中部地区、陇东区、陇南区和甘南区耕地压力均随经济的发展而不断增大,但各生态区耕地压力来源不同;河西区耕地压力的增大也与经济发展相关,但相关度不大,压力主要来源于生态环境的恶化及灾害的发生;最后针对各生态区不同的耕地压力来源,提出了耕地保护的策略。     

Comparative monitoring of temporal and spatial changes in tree water status using the non-invasive leaf patch clamp pressure probe and the pressure bomb

Real-time monitoring of plant water status under field conditions remains difficult to quantify. Here we give evidence that the magnetic-based leaf patch clamp pressure (LPCP) probe is a non-invasive and online-measuring method that can elucidate short- and long-term temporal and spatial dynamics of leaf water status of trees with high precision in real time. Measurements were controlled remotely by telemetry and data transfer to the Internet. Concomitant measurements using the pressure chamber technique (frequently applied for leaf water status monitoring) showed that both techniques yield in principle the same results despite of the high sampling variability of the pressure chamber data. There was a very good correlation between the output pressure signals of the LPCP probe and the balancing pressure values (on average r² = 0.90 ± 0.05; n = 8), i.e. the external pressure at which water appears at the cut end of a leaf under pressure chamber conditions. Simultaneously performed direct measurements of leaf cell turgor pressure using the well-established cell turgor pressure probe technique evidenced that both techniques measure relative changes in leaf turgor pressure. The output pressure signals of the LPCP probe and the balancing pressure values were inversely correlated to turgor pressure. Consistent with this, the balancing pressure values and the cell turgor pressure values could be fitted quite well by the same firm theoretical backing derived recently for the LPCP probe (Zimmermann et al., 2008). This finding suggests that use of the LPCP probe technique in agricultural water management can be built up on the knowledge accumulated on spot leaf or stem water potential measurements.     

不同工作姿态下立式双曲面网板水动力及周围流场特性研究

网板是单拖网中实现网具扩张的重要属具,其稳定状态直接决定拖网网口扩张程度,进而影响渔获效率和经济效益。该研究以立式双曲面网板为研究对象,利用水槽模型试验和数值模拟(Computational fluid dynamics,CFD)探究立式双曲面网板在不同倾斜状态(内、外倾斜,前、后倾斜)和冲角下的水动力性能变化,并对网板周围流场和表面压力进行可视化。结果显示:1)模型试验和数值模拟的网板升力系数均在倾角为0°,冲角为25°时达到最大值,分别为1.69和1.88;而两者的阻力系数均随倾角增大逐渐减小。2)模型试验和数值模拟的升阻比均随倾角增大逐渐减小;当内倾角为5°时,两者的升阻比均达到最大,分别为3.27和3.69。3)压力中心系数Cpb随倾角变化基本保持不变;但当网板处于前倾状态时,Cpc随倾角增大而增加;而网板处于后倾状态时,Cpc随倾角增大逐渐减小。4)CFD结果显示,网板中心面后部旋涡随倾角增大逐渐减小;当网板处于内、外倾状态时,前端流速衰减区随倾角增大逐渐增加;但当网板处于前、后倾状态时,衰减区随倾角增大逐渐减小;网板处于前倾状态时,压力中心随倾角增大逐渐向网板上端翼弦移动,网板处于后倾状态时则出现相反结果。研究结果可为今后研究网板稳定性和合理使用及调整网板提供科学参考。     

燃烧室背压对压力涡流喷嘴喷雾特性的影响

采用高速摄影技术、激光测粒仪和PIV测试技术系统试验研究了燃烧室背压对斯特林发动机压力涡流喷嘴喷雾形成过程、贯穿距离增长规律、喷雾锥角、液滴粒径和喷雾流场的影响。结果表明,燃烧室背压的增加使喷雾形状更加致密,贯穿距离的增加变缓,液滴平均速度增加,索特平均直径增加。当燃烧室背压大于1.0~1.5MPa之间的一个临界值时,其对喷雾锥角没有影响,小于此临界值,燃烧室背压的增加会使喷雾锥角急剧降低。     

沟槽滤嘴对中式低焦油卷烟主流烟气的影响

[目的]为中式低焦油卷烟设计中应用沟槽滤嘴提供一定的参考依据。[方法]研究不同透气度接装纸和不同吸阻沟槽滤棒对常规烟气成分、卷烟危害性评价指数的影响。[结果]尽管随着沟槽滤嘴中接装纸透气度或沟槽滤棒吸阻的增加,常规烟气成分、卷烟危害性评价指数均呈下降趋势,但对卷烟危害性评价指数中7种物质释放量的影响作用却有明显的异同。[结论]通过打孔接装纸和沟槽滤棒的配伍性,可以全面有效降低卷烟危害性评价指数中的7种物质,实现沟槽滤嘴在中式低焦油卷烟中的应用。     

邯郸市耕地资源压力动态变化及调控策略

根据1978～2008年相关数据,分析了邯郸市耕地-粮食-人口系统的动态变化,计算了耕地压力指数,并分析了该指数的动态变化及成因。结果表明:1978年以来邯郸市耕地面积及其人均量持续减少;粮食总产量及人均产量总体呈增加趋势;受其影响,最小人均耕地面积和耕地压力指数呈现相似的变化趋势。最后探讨了缓解耕地压力的调控策略,指出保持区域内一定数量的耕地、种植高产作物、严格控制人口增长是缓解耕地压力的重点。     

隔舌间隙对双吸离心泵内部非定常流场的影响

为了研究隔舌间隙对双吸离心泵内部非定常流场的影响,采用大涡模拟方法和滑移网格技术,对双吸离心泵在设计工况下的内部湍流进行了数值计算,重点分析了5组隔舌间隙下泵内非定常流场特性及压力脉动特性.结果表明:随隔舌间隙增大,水泵扬程整体呈上升趋势,效率则整体呈下降趋势;蜗壳内压力脉动频率以叶片通过频率为主,主频和压力脉动幅值均随隔舌间隙的增大呈减小趋势,隔舌间隙增加4％时,隔舌位置1倍叶片通过频率处的脉动幅值降低9％左右;叶片区压力脉动频率以叶轮转频为主,最大压力脉动幅值均出现在2倍叶轮转频处,当隔舌间隙比设计隔舌间隙减小4％时,叶片正面中心位置2倍叶轮转频处压力脉动幅值增加约38％.